The stand-by time is solely dependent on how long the last person in line is willing to wait. If someone doesn't want to wait an hour for an attraction, then he doesn't get in the one-hour-wait line.
One's tolerance for waiting is based on: repetitive quality of attraction, estimated number of days until next visit to the park, and overall social changes in patience.
The length of the stand-by queue for a specific wait time is dependent on the FP:stand-by ratio and the number of FP returnees during the wait.
Source: Operations and Logistics thoughts unfiltered from my head.